• It is the process of forcing out the burnt exhaust gases from the cylinder for admitting the fresh charge into the cylinder.
• This action takes place in the two stroke cylinder.
• The charge (air fuel mixture or air) enters the engine cylinder from the crank case at a pressure higher than the exhaust gases.
• This fresh charge forces the exhaust gases to the atmosphere through the exhaust port.
• During the period both the transfer and exhaust ports are kept open for a short period.
• Hence there is a possibility of the fresh charge escaping out with the burnt gases.
• This is over come by designing the piston to have a deflected shape.
• This shape of piston deflects the fresh charge upward in the engine cylinder.
• It also helps out in forcing out the exhaust gases to atmosphere.
• This process is known as Scavenging.
• Heat Engine is a machine which converts heat energy supplied to it into mechanical work.
• Heat energy is supplied to the engine by burning the fuel.
Piston rings :
Piston rings are inserted in the grooves provided in the piston. Two types of piston rings are used in the piston.
1. Compression rings
2. Oil rings or oil control rings